Antibiotic Medium No. 1

Antibiotic Medium No. 1

Official Standardized Assay Medium for Antibiotic Potency Testing

Catalog Number: AS-1108

Overview

Antibiotic Medium No. 1 is the globally recognised standard solid medium used for antibiotic potency determination by cylinder-plate (cup-plate) and turbidimetric microbiological assay methods. Originally developed by Grove and Randall (1955), it is specified as “Medium A” in FDA (21 CFR 436.102), USP <81>, European Pharmacopoeia 2.7.2, Japanese Pharmacopoeia (JP 17), WHO, and ISO 20776-2 standards.

The formulation provides optimal growth conditions for commonly used test organisms, ensuring sharp, well-defined, and highly reproducible inhibition zones, which are essential for accurate antibiotic potency assessment in regulated pharmaceutical laboratories.

Key Features & Benefits

Globally harmonised formulation (USP / EP / BP / JP / WHO / ISO)

Produces sharp and reproducible inhibition zones

Low inter-laboratory and batch-to-batch variability

Recognised reference medium for regulatory antibiotic assays

Suitable for both agar-diffusion and turbidimetric methods

Typical Applications

Pharmaceutical Quality Control
Microbiological potency assay of antibiotics including:
penicillins, tetracyclines, aminoglycosides, macrolides, and others

Routine batch release and stability testing

Cylinder-Plate & Agar-Diffusion Assays
Standard medium for cup-plate diffusion assays

Used as seed agar or base agar depending on method design

Turbidimetric Assays
Seed medium for turbidimetric antibiotic assays

Growth response measurement for potency determination

Principle of the Medium

Antibiotic Medium No. 1 provides a balanced nutrient base that supports uniform growth of sensitive indicator organisms. Antibiotics diffuse evenly through the agar, producing inhibition zones whose diameter is directly proportional to antibiotic concentration, enabling precise and reproducible potency calculation.

Typical Composition (per litre)

Beef Extract – 1.5 g

Yeast Extract – 3.0 g

Peptone (meat or casein) – 6.0 g

D-Glucose – 1.0 g

Agar – 15.0 g

Final pH: 6.6 ± 0.1 at 25 °C (after sterilisation)

Preparation

Suspend 26.5 g of dehydrated medium in 1 L purified water

Heat with frequent agitation and boil for 1–2 minutes until fully dissolved

Dispense as required

Sterilise by autoclaving at 121 °C for 15 minutes

Cool to 45–50 °C for pouring

Typical layer thickness:
1–2 mm base layer
3–4 mm seeded layer containing test organism

Storage & Stability

Dehydrated medium: Store below 30 °C in a cool, dry place

Prepared plates: Store at 2–8 °C, protected from light and desiccation

Recommended use within 7 days

Standard Test Organisms

Staphylococcus aureus ATCC 6538P / NCTC 7447

Bacillus subtilis ATCC 6633

Kocuria rhizophila ATCC 9341

Bordetella bronchiseptica ATCC 4617

Intended Use

For laboratory and pharmaceutical quality-control use only.
Not for clinical diagnostic, food, or veterinary applications.

Quality & Compliance

Legally recognised standard medium for antibiotic potency assays

Complies with USP <81>, EP 2.7.2, JP 17, WHO, FDA, and ISO requirements

Manufactured under controlled conditions for batch consistency

COA, SDS, and TDS available upon request

Customs & Trade Information

HS / AHECC Code: 3821.00.00
Prepared culture media for development or maintenance of microorganisms